On the presence of oxyphosphorus bonds in TOPCon solar cell polycrystalline silicon films

The presence of silicon oxyphosphorus bonds in the heavily phosphorus (P)-doped n+-type polycrystalline silicon film (n+-poly Si) of TOPCon solar cell has been mainly revealed through a depth-profile X-ray photoelectron spectroscopy (XPS) characterization of chemical components. X-ray diffraction (XRD) pattern is applied to the verification of recrystallized phases in the n+-poly Si film, while high-resolution transmission electron microscopy (HR-TEM) with energy dispersive X-ray (EDX) pattern is used for distinguishing the crystallinity and the elemental segregation. The test sample is of a typical rear passivation contact stacks of c-Si/SiOx/n+-poly Si/SiO2, in which the n+-poly Si layer is heavily phosphorus-doped by ion implantation of as-deposited intrinsic thin film through low-pressure chemical vapor deposition (LPCVD) and recrystallization at 900 °C afterward. In the whole n+-poly Si layer, XPS P 2p electronic states at 129.8, 133.4 and 136.8 eV have been detected and assigned to be Si–P (or P–P), O–P and P–O–P bonds, respectively. In addition, the thermodynamic functions, such as the Gibbs free energy and mole formation energy of likely chemical bonds under the lowest energy as well as temperature-composition fraction (T-CF) phase diagram, are also implemented in the verification of the derivatives of phosphorus oxides.